1. Field of the Invention
This invention relates in general to methods and apparatus for the transfer and reproduction of half-tone pictures utilizing rastered processes and in particular to a novel method and apparatus for breaking up the picture elements.
2. Description of the Prior Art
In conventional reproduction systems for transferring pictorial or written material, the pictorial or written material which is to be reproduced is attached to a plane or cylindrical surface. This is called setting up the system. The original to be reproduced is then optically-electrically scanned and the electrical values associated with each of the elements of the picture are determined for the purpose of preparing the printing matrixes as for example, in offset printing processes or for engraving printing rollers. If half-tone pictures are to be produced the dimensions of the original pictures rarely coincide with the desired size of the pictures to be reproduced. In this event, the original pictures are normally enlarged or reduced to the desired scale by the use of photographic processes.
Frequently the picture original is a transparent diapositive miniature or even microfilm taken from a storage archives.
Another reproduction technique of half-tone pictures which has been frequently used has been to obtain recording data of half-tone pictures not only at the time of reproduction by means of optically scanning the original, but to do this before the reproduction is to occur and store the electronic data from the scanning process in a suitable memory device so that they will be available for picture reproduction at a later date.
Thus, it is known to optically electrically scan a picture for the purpose of changing the scale, to quantize the scanned signals, to store them digitally and to read them from the memory at a different timing rate than that in which they were read into the memory. This allows an expansion or compression, in other words, an enlargement or reduction and such a system is described, for example, in U.S. Pat. No. 3,272,918. However, in such system, after the information is read out from the memory, the picture signals are again changed back into analog signals and are recorded as such, which means that no rastered reproduction results.
U.S. Pat. No. 3,688,033 discloses a method for setting rastered half-tone pictures (the original picture signals are digitized). Depending on the brightness of the scanned value of the original, the recorded data for the picture element configurations which were separately prepared and scanned for each tone value prior to scanning the original, are then recalled from a separate memory and recorded. The scanning of such picture element configurations on a true to scale picture element basis may be accomplished as described in U.S. Pat. Nos. 3,652,992 and 3,710,019, for example.
An improvement of this procedure is disclosed with the raster rotation in multi-color printing processes in U.S. Ser. No. 124,864. A recording of the picture elements may be accomplished by the use of a cathode ray oscilloscope and then recorded on film material as described in U.S. Pat. No. 3,688,033 by means of an engraving member; for example, a stereo type heliograph available from the assignee of the present invention. Other means such as the use of suitable light sources such as described in U.S. Pat. Nos. 3,657,472 and 3,725,574 are particularly suited for the raster scanning and recording of color component images in multi-colored printing.
It is common in all methods using rastered scan recording processes to use puncti form spots as the so-called picture elements or raster points which are set equi-distant in a network-like arrangement. The distances between the picture elements are so small that they cannot be distinguished individually with the naked eye. In practice in conventional rastering, the size of these elements is 30 points per centimeter which is defined as "raster size 30". In cases where more refined rastering is required, up to approximately 60 points per centimeter "raster size 60", can be used. These raster points provide picture elements which can be regarded as p points of concentration of the defined raster network, which in a particular example could comprise squares having a dimensions of 0.33 mm. Another example squares having dimensions of 0.167 mm can be utilized.
The scanning process for the purpose of obtaining the electronic data is accomplished in a known fashion with the aid of an opto-electrical scanner which measures the gray values of the individual picture elements of the picture and converts them to analogous electrical voltage values. In order to store the electrical data, these analogous values are quantized and coated and placed in a memory as binary numerical values.
In order to obtain a sufficiently fine gradiation of the gray values, the number of the quantum stages -- i.e., the stages during the quantizing must be quite large. Thus, in order to store the gray value of a particular point element, a storage cell of bit size if required.
The stored picture consists of a fixed number of stored scanning data of the gray values of the individual picture elements. Since their number is dependent upon the raster used, the entire data complex is assigned to a specific picture scale. In order to reproduce pictures at other scales, pictures with the altered scales corresponding to the required raster size would have to be prepared by a photographic method prior to scanning. In order to be able to satisfy all scale requirements, required for later reproduction of pictures, it would be necessary to prepare many similar pictures in varying enlargements and with corresponding rastering, to then scan them and to record them and store such recorded data in a storage archive. Such a method would be time consuming and costly and would, in practice, require very large storage spaces.